Polarized, two-wire, progressive, noninterfering signal system



Oct. 21, 1941. M. w. MUEHTER 2,259,960

, PROGRESSIVE, NONINTERFERING SIGNAL SYSTEM POLARIZED, TWO-WIRE .Ml liI. m A w INVENTOR: iynsdW/WefiZei; BY I MA A1 TORNEY.

EDFUUBUD QZDOEV Patented Qct. 21, 1941 POLARIZED, TWO-WIRE, PROGRESSIVE,NONINTERFERING SIGNAL SYSTEM Manfred W. Muehter, Nutley, N. J., assignorto American District Telegraph Company, 1110., Jersey City, N. J.,' acorporation of New Jersey Application September 21, 1937, SerialNo.164,887

26 Claims. (01. 177-361) This invention relates to electric signalsystems and transmitters and receivers therefor, and more particularlyto systems wherein a large number of transmitters on the same circuitare prevented from interfering with each other, and are successivelyoperated when more than one are waiting at the same time to operate,though it is noted that in some of the claims the invention is notlimited to systems of the non-interfering type.

One object of the invention is to provide an improved system of thiskind in which the transmitters are provided with motors operated fromthe central source of current at the receiving station, and wherein themotor is operated by current impulses and operates means for varying thestrength of these impulses for sending code Signals.

Other objects of the invention are to provide,

in a system of this kind, improved signal means for indicating groundsand line breaks.

Additional objects of the invention are to improve generally thesimplicity and efficiency of such systems and apparatus and to providean apparatus of this kind which is reliable in operation, and economicalto manufacture and install.

Still other objects of the invention will appear as the descriptionproceeds; and while herein details of the invention are described in thespecification and some of the claims, the invention is not limited tothese, since many and various changes may be made without departing fromthe scope of the invention as claimed in the broader claims.

The inventive features for the accomplishment tively from the first andsecond terminals of a current source, at a control station, and thencepast a plurality of transmitters, the lines being connected by aresistance at the outer ends.

Each transmitter comprises a motor and a starting means for starting themotor, which is adapted to be connected through a rectifier between saidlines. A code means is operated by the motor to connect said linestogether through unequal resistances alternately; and means operated bysaid motor connects the lines and breaks the one line beyond theconnection, thereby to change the rate of current flow in the lines atthe control station. Said current change sets in operation a motorcurrent supply means, and a reversing means for reversing the connectionof said lines with the source to change the polarity. A marginal codingmeans is provided atthe control station in circuit with one of saidlines.

The change in polarity prevents the starting means for othertransmitters from receiving current for starting their motors, thus toprevent interference. The break beyond said connection established inthe started transmitter shuts out more remote transmitters. Thus when aplurality of transmitters are waiting to start, the one nearest thecurrent source can start first.

In the accompanying drawing showing, by way of example, one of manypossible embodiments of the invention, the figure shows a diagram of thewhole system, the normally disengaged contacts being shown in outlinewith uninked intra-marginal part, while the normally engaged contactsare shown in solidblack throughout.

1 The supervisory system The line circuit of the system is normallysupervised for breaks and grounds. The supervisory circuitcan be tracedfrom plus through relay winding RI throughthe left hand winding of breakdetector relay 13, contact 2 of relay U through line R and the varioustransmitters 5, 6, I connected to the line. The internal circuit throughthe :transmitter' 5 can'be traced from terminal Ra through conductor 8back contact Mb of cam contact assembly M, back contact Ab, outgoingterminal Rb. At the end of the line a resistor REZ connects-the R. lineto the L line. The supervisorycircuit extends through the L line back tothe central station, then through contact 4 of relay U, right handwinding of relay B, the winding of relay R2, conductor ID to minusbattery. The two windings of break detector relay B are arranged to add,holding this relay energized by the supervisory current. If a break inthe line occurs, relay B .deenergizes and'gives an indication by closingits back contact to a buzzer or light (not shown).

For ground supervision, relay G is provided connected to the center ofbattery I l and through contact 8,0f relay U to a ground. If a groundoccurs on either of the'two line wires R or L, current will flow throughthe ground relay G and operate it, giving an audible or visibleindication.

The transmitters Each transmitter consists of a" step by step device Soperated by two individual magnets Sa, Sb, so arranged that theassociated ratchet wheel I2 is advanced by the pawl I2 on the release ofthe spring retracted member l3 having a lost motion connection I4 withthe armature I which is common to the two magnets. The ratchet wheeldrives two control cams m and t and a code wheel 0. The armature inaddition to operating the ratchet wheel operates armature contact Aduring its initial motion. The lost motion arrangement insures that themain load represented by the ratchet mechanism I2, I 2' is not picked upuntil after the operation of armature contact Ab, for reasons which willbe apparent later.

The device that is supervised by each transmitter is arranged to operatea singlejp'ole, double throw switch D, shown in the normal condition. Ifan abnormal condition occurs, the transfer elerelay P and contact #3 ofrelay Q through conductor 23 to plus, thus energizing relay U after ahalf cycle of the operation of relays P and Q.

'the line circuit is open at this particular time causing thetransmitter step device S to release its i armature and advance theratchet wheel and asment of switch D is actuated to the other posivtion, closing a circuit for the ep'emuontr the associated transmitter.This canbe traced as follows: from plus battery through relay-windingRI, left hand winding of relay B, contact 2 of relayU, line R, throughintermediate transmitters if they are interposed between thecentraloffice and the transmitter under consideration, through resistance REI,a cold cathode vacuum tube I8, terminal SI, the normally open side dI ofswitch D, conductor 112, back contact Tb of cam contact assembly T, backcontact Cb of the code wheel contact assembly C, left hand magnet coilSb to line L from which minus polarity is obtained through contact 4 ofrelay U, right hand winding of relay B and the coil of relay R2. Thisprovides the ignition circuit for the-cold cathode tube I8 which startsthe current through the main gap thereof which is shunted aroundresistance REI.

'This current may or may not be of sufficient intensity to operatemagnet S completely. How'- ever it is capableof causing contact Ab, A tobe operated. The normally open contact A), now closed, shunts the .coldcathode tube, through conductor 8, contacts Mb, A,f,conductor I9,contact Cb, coil Sb, thereby eliminating the tube from the circuit."Contact Ab, onopeni'ng, breaks the line L beyond the transmitter 5preventing other transmitters 6, 'I" further on the line from starting.7 a

Control station operation The increased'current caused by the connectionof magnet S in the line circuit operates primary marginal relays'RI andR2 which close contacts of both relays RI and R2 is necessary to operaterelay ST. This is toprevent a false start if an accidental ground shouldcause a current strong enough to operate one of these relays.

Relay ST operates, shunting out the coils of relays B, RI. and R2, andlocks in" to' minus through its contact 'I andicontact 5 of relay U andcontacts I of relays P and Q in multiple,'and also closes its contacts2* and 3, thus shunting out the coils of relays B, RI and R2. Contact 4of re lay ST closes a circuit from plus through a resistor ZI,ith'ewinding ofmain pulsing relay P to negative, energizing'thisrelayJ Whencontact 3 of relay P opens auxiliary pulsing relay Q becomes not shuntedand ,can likewise operate through resistor 22 and an obvious circuit.Re- "lay Q by closing its contact 2 shunts the coil of relay P causingit to deenergize after a short interval of time. As relay P closes itscontact 4, reversing relay U is energized from minus throughconductorlfl', the coil of relay U, contact 4- of sociated cam shaft 39one step.

The step device operates the master cam contact assembly Mto closenormal open contact M),

establishing a permanent shunt through conductors 8' and 9 and contact Caround the tube and opening the line R beyond the transmitter.Subsequent operation of armature contact A will have no result. a

After a short interval of time the shunt across the coil of relay'Qapplied by contact 3 of relay P becomes effective, causingrelay Q torelease. This relay opens its contact 2 allowing relay P to reenergize.This completes one cycle of the operation of relays P and Q whichcontinue to operate in themanner described above for the duration of thesignal transmitted. When relay P picks up subsequent to the operation ofrelay U, negative polarity is applied to the line R through contact 2 ofrelay P, right hand winding of relay ST through the coil of relay K andcontact I of relay U again completing the circuit for the transmitter.It will be noticed, however, that because of the operation of contacts Iand 3 of relay U, the currentfiowing is of opposite polarity. Thepurpose of this is to prevent from starting other transmitters locatedbetween the operating transmitter and the central ofiice; as current ofopposite polarity will be prevented from flowing by the associated coldcathode tube I8'of any of said other transmitters which tube only passescurrent in one direction. Other types of rectifiers I such, forinstance, as those of the copper oxide type or other suitable type couldalso be used for this purpose. V

' Transmitter operation I As impulses from relay Pare transmitted to theactuated transmitter, its cam shaft will be advanced step by step. Thecode is transmitted in accordance with the teeth of its code wheel whichoperate the transfer element of contact C when the associated pen springis thrown up by a tooth. In that case, the right hand magnet coil Sa iscut in through conductor 3! instead of the left hand magnet coil Sb.-This magnet coil Sa is capable of causing the stepping of ratchet wheelI2, but has a much lower resistance and thereby increases the currentfiow in the coding circuit to such a value that relay K is operated andclosing its contact I operates the recording register 32 through anobvious circuit. The code as represented by the code wheel will therebybe recorded on the register.

It will be noticed that the locking circuit for the left hand winding ofrelay ST is open when both contacts I of relays P and Q are open, whichoccurs during the transmission of a line impulse. At this time, relay STis dependent on the line current flowing through itsright hand windingand relay K for retaining its armature energized. In the illustratedtransmitter, the code wheel 0 is provided with twosets of teeth,

each characteristic of the device controlling switch D, the second sethaving an additional tooth or group of teeth representing therestoration of the device to normal.

When the transmitter has completed its first signal, the cam m has moveda half rotation and the notch m2 allows the contact M to restore tonormal position. The starting circuit through contact Tb is likewiseopen as contact T has been transferred by cam t to the abnormal side Tiduring the transmission of the signal, con necting the transfer elementof contact T with contact d3 of switch D. The line circuit within thetransmitter is now restored to the normal condition. The next impulsetransmitted over the line from relay P will only energize the endof-lineresistance REZ. This current is too weak to maintain relay ST energizedthrough its right hand winding and the relay releases opening itscontact 4, deenergizing relays P and Q. Re-

lay U deenergizes when relay Q releases and opens its contact 3.

Release of relay U also restores the normal supervisory circuit. Othertransmitters are now able to transmit their signal in a similar way.

When the device switch D is restored to contact d3 the normal condition,the associated transmitter is operated again but through the normallyopen side T of cam contact T. The operation is otherwise the same exceptthat a slightly different code is transmitted by the corresponding sideof the code wheel to indicate the restored condition.

It will be noted that the ground detector G is disconnected duringtransmission of a signal by the opening of contact 8 of relay U. Thispermits operation of the system with a ground on the line. A break onthe line will affect transmitterslocated beyond the point of the break;but other transmitters will still be able to send signals.

The purpose of contacts 6 and I of relay U, contact 4 of relay P, andcontact 3 of relay Q is to energize relay U after half a cycle ofoperation of relays? and Q so as to insure a proper starting impulse forthe transmitter on the line before the current is interrupted. Thesecond purpose is to have relay U release at the end of the signal atthe moment when relays P and Q have completed their cycle so as to besure that a new signal coming in immediately will start with the relaysP and Q in their normal condition and that the time delay for thestarting operation will be always the same.

I claim as my invention:

1. In combination, a source of direct current; a series of transmitters;first and second lines extending from the first and second terminals ofsaid source past said transmitters; marginal relays .having their coilsin the respective lines near said source; each transmitter including aone-way rectifier, a motor operatedby impulses, means to connect saidlines through the rectifier to start the motor, motor operated means tochange current flow in the lines to operate the marginal relays, and acodemeans operated by the motor to vary the current in said lines;starting means operated by the marginal relays;

pulsing means set in operation by the starting relay; a coding relayconductor having therein a marginal codingrelay; a reversing relayenergized by the operation of the pulsing means and having means todisconnect the first line from first terminal and connect it to oneendofthe coding relay conductor, and disconnecting the second line fromsecond terminal and connect it to the first terminal; an interrupteroperated by the pulsing means for intermittently connecting the otherend of the coding relay conductor to the second terminal to cause themotor to intermittently release its armature.

2. In a signaling system, a loop circuit including a transmitter and asource of potential, a pair of cooperating relays connected to saidsource for supplying driving pulses to said transmitter, a grounddetecting relay connected between said source and ground whereby aground in said loop energizes said ground detecting relay, meansincluding a switch for starting said transmitter and means responsive tooperation of said switch and one of the pulsing relays for opening theground connection to said ground detecting relay.

3. Ina signaling system, a transmission line including a transmitter anda source of potential, a pair of cooperating relays connected to saidsource for supplying driving pulses to said transmitter, means connectedbetween said source and ground and responsive to ground conditions insaid transmission line, means connected in circuit with said transmitterfor starting the same and means responsive to operation of saidtransmitter starting means and one of the pulsing relays for removingthe ground connection to said ground responsive means wherebytransmission of signals is not interfered with by a ground in thesystem. 7

4. In a signaling system, a loop circuit including a transmitter and asource of potential, a ground detecting relay connected between saidsource and ground whereby a ground in said loop energizes said grounddetecting relay and means for controlling said transmitter, saidcontrolling means including a pair of primary starting relays connectedone in each side of said loop for completing a starting circuit for thetransmitter whereby a ground in one side of said loop effective toenergize only one of said starting relays does not cause falsetransmitter operation.

5. In a signaling system, a transmission line including a transmitterand a source of potential, means connected between said source andground for detecting ground conditions in said transmission line, meansfor starting said transmitter in response to a change in the current insaid line andmeans connected in circuit with said transmission line forpreventing false operation of said starting means upon the occurrence ofa ground condition in said transmission line.

6. In a signaling system, a transmission line including a transmitterand a source of potential, means connected between said source andground for detecting groundconditions in said transmission line, meansfor starting said transmitter, relay means connected in circuit withsaid transmission line for preventing said transmitter from startingupon the occurrence of a ground condition in said transmission line, andmeans responsive to said starting means for removing the groundconnection to said ground detecting means upon the occurrence of asignaling condition on said transmission line.

7. In a signaling system, a two-wire loop circuit including atransmitter and a source of potential, a break detecting relay connectedin series in said loop circuit whereby a break in said loop circuitcauses deenergization of said break detector and a break signal andswitch means for reversing the polarity of the loop circuit and oftransmission of a signal. 7

8. In a signaling system, a loop circuit having at least. twotransmitters therein, a central sta' tion including a recorder and asource of potential connected to said loop, a pair of normallyunoperated marginal relays connected at said central station, one ineach side of said loop, a rectifier tube connected to one side ofeachtransmitter, a magnetically operated switch connected to the other sideof each transmitter, means including a. stepping magnet for operatingsaid switch and transmitter, a switch connected between said rectifierand said magnet for establishing a circuit through said rectifier tooperate .said magneticallyroperated switch and shunt the extendedportions of said loop beyond the operatedtransmitter whereby the currentin. the connected portion of the loop increases,- contacts operated bythe stepping magnet for shunting said rectifier and further increasingthe loop current, a start circuit including a main starting relay andthe contacts of said marginal relays and energized by the increasedcurrent resulting from actuation of said magnet, a switching magnetactuated by said startingrelay'for changing the polarity of thepotential connected to said loop whereby every rectifier at saidtransmitters ceases to function and prevents connection of othertransmitters; a pulse transmitter connected to said loop by saidswitching magnet for driving said transmitter step by step through saidstepping magnet, a second magnet at said transmitter having a lowerresistance than the stepping magnet, a code wheel at said transmitter,cam operated switch means for connecting'the contacts operated by saidwheel and said second magnet in series and across said loop wherebyimpulses of greater than normal value are transmitted to said centraloflice, a marginal coding relay in said loop responsive to said codeimpulses for energizing said recorder in accordance with the transmittedcode.

9. In a signaling system, a loop circuit having at least twotransmitters therein, a central ofiice including'a recorder and a sourceof potential connected to said loop, a unidirectional device connectedto one side of each transmitter, switching means at each transmitter forestablishing a circuit through said device and shunting the outerportion of said loop. beyond an operated transmitter whereby the currentin the connected portion of said loop increases to start thetransmitter, means operated: bythe transmitter to furtherincrease theloop current, a marginal starting circuit at saidcentral ofiiceresponsive to the change of current in said line, means to change thepolarity of the potential across said loop in response to actuation ofsaid starting circuit whereby every unidirectional device at thetransmitters in the connected portion of said loop ceases to function, apulse transmitter connected to said loop in response to the closure ofsaid starting circuit for driving the operating transmitter, meansatsaid transmitter for changing the current value in said loop, a codewheel in said transmitter for controlling said means to transmit codeimpulses and amarginal means responsive to code impulses for operatingsaid recorder.

10. In a signaling system, a transmission line having at least twotransmitters connected therein, a central office including a source ofpotential connected to said line, means for initiating operaremovingsaid' break detector from the operating circuit of said. transmitterupon the occurrence tion of a transmitter in response to-signalingcondition, means responsive to initiation of operation for disconnectingthe outer portion of said transmission line, unidirectional devicesconnected between the other portion of the transmission line and each ofthe transmitters therein, means at the central ofiice for changing thepolarity of said transmission linein response to operation of saidtransmitter whereby the transmitters in said other portion of thetransmission line are rendered inoperative by said unidirectionaldevices and means for shunting the rectifier at the operatedtransmitting station whereby it ismaintained operative.

11. In a signaling system, a transmission line having at least twotransmitters therein, a source of potential connected to saidtransmission line, means for initiating operation of a transmitter inresponse to a predetermined signal condition, means responsive toinitiation of operation of said transmitter for disconnecting the outerportion of said transmission line whereby transmitters in said outerportion are disabled, and a unidirectional means associated with eachtransmitter for disabling idle transmitters in the other portion of saidtransmission line whereby interference between transmitters iseliminated.

12. In a signaling system, a two conductor line having at least twotransmitters therein, a source of potential connected to saidconductors, a unidirectional means associated with each transmitter,means including said unidirectional means for initiating operation of atransmitter in response I to a predetermined signal condition, meansresponsive toinitiation of operation of said transmitter forinterrupting the outer portion of said two conductor line beyond theoperating transmitter whereby transmitters in said outer portion aredisabled, and means responsive to initiation of operation of saidtransmitter for reversing the connection of said line to said source toreverse the polarity of said two conductor line whereby theunidirectional devices become effective to disable the remaining idletransmitters in said line to eliminate interference betweentransmitters. 1

13.. In a signaling system, a-transmission line including a transmittertherein, a central oflice associated with said transmission line, meansto initiate operation of. said transmitter, means responsive thereto forchanging the current in said transmission line-to createacontrol'condition,means at said central office responsive to saidcontrol condition to start operation of said transmitter, meansresponsive to said starting operation for sending code by currentconditions differing from the control condition and means at saidcentral oflice responsive to the different current conditions forreceiving code signals.

14. In a signaling system, a transmission line having a transmittertherein, a central office including a recorder and a source of potentialconnected to said loop, means in each of said transmitters for settingup a control condition in said transmission line, a pair of normallyunoperated marginal relays connected at said central station, onein'seriesrelation with each side of said transmission line, a marginalcodingrelay, a starting circuit at said central station including a mainstarting relay connected to the contacts of said pair of marginal relaysand across said source of potentialand responsive tov said controlcondition created at a transmitter, a pulse transmitter at said centralstation, means for initiating the operation of said pulse transmitter inresponse to operation of said starting circuit, means including saidpulse transmitter for establishing a circuit through said main startingrelay, said line, said source and said marginal coding relay and forestablishing a change of polarity in said trans-- mission line, andmeans at an operated transmitter for changing the current condition insaid transmission line in accordance with code signals for controllingsaid marginal coding relay to cause said recorder to receive signals.

15. In a signaling system, a transmission line having a transmittertherein for generating code impulses having certain characteristics, acentral oifice including a recorder and a source of potential connectedto said transmission line, means in each side of the transmission lineat said central ofiice responsive to predetermined current conditions, astarting circuit including said means and responsive to a line-currentcontrol condition created at said transmitters, means controlled by saidstarting circuit for reversing the polarity of said transmission lineand initiating transmission of coded signals from said transmitter, andmeans responsive to the signals for controlling 'said recorder inaccordance therewith.

16. In a transmitter, a motor comprising a pair of operating coils, onehaving less resistance than the other, a stepping mechanism, an armatureengaging the stepping mechanism and having lost motion with respectthereto and driven by said coils, a pair of contacts adapted to beoperated by said armature in predetermined time relation to operation ofsaid stepping mechanism, a first cam and a first pair of cooperatingcontacts operated by said stepping mechanism, a second cam and a secondpair of cooperating contacts operated by said stepping mechanism, a codewheel having teeth thereon and a third pair of contacts associatedtherewith and operated by said stepping mechanism, a normal line circuitextending through one contact associated with said first cam and onecontact associated with said armature whereby the line is normallyclosed around said transmitter, an initial starting circuit completedonly under predetermined conditions including a rectifier, a startingswitch, the normally closed contact associated with said second cam, thenormally closed contact of said code wheel and one of said operatingcoils whereby the contact associated with said armature is opened tobreak the line circuit, the connection of the coil varies the current inthe circuit to cause a control signal, and said rectifier is shunted bya contact associated with and operated by said armature wherebyoperating current of opposite polarity can flow and a transmittingcircuit which is closed through a contact associated with said codewheel, a contact associated with said first cam and the second operatingcoil whereby the code is transmitted at a different current value whenthe stepping mechanism is actuated.

17. In a transmitting system, a line circuit, a first resistance, asecond resistance having a different value, means including aunidirectional device responsive only to a predetermined condition inthe line circuit for establishing a circuit through said firstresistance and the line circuit to accomplish a control condition of thesystem and means responsive to said control condition for shunting saiddevice and establishing a circuit including the line circuit and saidsecond resistance for generating a signal in the line circuit.

18. In a transmitter, a motor comprising a pair ofoperating coils, onehaving less resistance than the other, a' stepping mechanism controlledby said motorpswitching means controlled by said stepping mechanism forinserting one of said coils in an operating circuit to create adistinctive current condition for accomplishing a control function, asecond switching means controlled by said stepping mechanism in responseto said control condition'for connecting a second coil in an operatingcircuit to create a second current condition, and acoding means operatedby 'said' stepping 'mechanism for making and breaking the circuitthrough said second coil to utilize said second current condition forthe purpose of transmitting coded signals.

' 19. In a transmitter, a motor comprising a pair of operating coils,one having less resistance than the other,a stepping mechanismcontrolled by said coils, a switch controlled by said steppingmechanism, means including a rectifier in circuit withsaidswitch adaptedto conduct current of predetermined polarity whereby said transmittercan operate. onlyjunder predetermined conditions of polarity, a secondswitch controlled by said stepping mechanism for connecting one of saidoperating coils in circuit to create a control condition when thepredetermined polarity condition exists,.means responsive to saidcontrol condition for shunting said rectifier and connecting a secondoperating coil in an operating circuit tocreate a distinctive currentcondition, and a coding device operatedby said stepping mechanism formaking and breaking the circuit through said second operating coil totransmit a coded signal by means of the distinctive current conditionscreated by said operating coil.

20. In a signaling system, a transmission line including a plurality oftransmitters and a source of potential therein, each transmitterincluding an initiating switch, a rectifier and a motor in series withsaid source whereby operation of said switch energizes'said motor, aswitch operated by said motor for disconnecting said motor, a switchoperated by said motor for disconnecting the outer portion of said linefrom said transmitter, switch means responsive to energization of saidmotor, a pair of parallel connected pulsing relays connected across saidsource by the switch means and having contacts in said line and othercontacts for alternately shunting each other whereby they operate inalternation, a transfer relay for reversing the connection of saidsource to the line whereby said rectifier in each transmitter ceases tofunction, a contact closed by the release of the first one of saidpulsing relays and a second contact closed when the second pulsing relayis energized for energizing the transfer relay after one half anoperating cycle of the pair of pulsing relays and a second contactopened by said first pulsing relay for opening said line circuit tooperate said motor and shunt the rectifier at the operative transmitterto start the transmitter.

21. In a signaling system, a transmission line, including a transmitterand a source of potential, initiating means for transmitting a startingimpulse from said transmitter, means including an interrupter responsiveto said starting pulse for driving said transmitter, and means wherebythe initiating means does not operate unless the line is closed.

22. In a signaling system, a transmission line including a plurality oftransmitters and a source of potential, means for initiating operationof each transmitter, means responsive to the initiating means fordisconnecting the outer-portions of saidtransmission line andconnectin'gthe operat'- ing transmitter across said line, means connect= ed to saidline in response to said connection for operating a connectedtransmitter and means responsive to said last=mentioned means fordis=abli'ng' the initiating means whereby only the op erating transmittercan operate. I,

23. -In a signaling system, a twoewire trans= mission line including aplurality of transmitters and a source of energy, initiating means ateach transmitter including a switch; a rectifier and a motor forconnecting an operating transmitter to said line and disconnectingremote transmitters, starting means responsive to operation of theinitiating means, a pulse transmitter 'responsive to the startingmean'sfor driving said motor, switching means responsive to the pulsetransmitter for reversing the polarity of said line with respect to saidsource of energy whereby the initiating circuits of said transmittersare disabled, code transmitting means operated by said motor, camoperated means driven by said motor for connecting said code 'means'tothe line for transmitting an alarm signal, switch means operated bysaidcarn for controlling the starting means to restore the entirecircuit to normal after the transmission of an alarm signa anq a'second'cam means operated the motor for preparing another initiatingcircuit whereby restoration of the first-mentioned switch at theoperated transmitter to its normal position will start the transmissionof 'a restoration signal.

24. In a signaling system, a transmission line,

a plurality of transmitters and a source of current connected thereto,means including an initiating circuit for each transmitter fortransmitting a starting signal over said line, means connected to saidline in response to said starting signal for operating the activetransmitter to send analarm signal and means for conditioning saidtransmitter whereby it will send a restoassess-o ration signal When-saidinitiating circuit is restored to normal.

'25. in a signaling system, a twoconductor transmission line, aplurality of'transrnitter's and a source of current therein,meansvincluding an initiating circuit in each transmitter for'di'sconnecti'ng'one of said conductors and connecting the transmitter acrossthe line whereby transmitters in said one conductor beyond an activetransmitter are disabled, polarity responsive means in each initiatingcircuit and means responsive to connection of a transmitter to reversethe con -ne ction of said source to said line whereby the polarityresponsive means in idle transmitters connected to the other of saidconductors becomes effective to disable said last-mentionedidletra'nsmitters.

26. In a signaling system, 'a two-conductor transmission line, aplurality of transmitters and a source of current therein, meansincluding an initiating circuit in each transmitter fordisconnecting'one of said conductors and, connecting the transmitteracross the line whereby transmitters in said one conductor beyond anactive transmitter are disabled, polarity responsive means in eachinitiating circuit, means responsive to connection of a transmitter toreverse the connection of said'source to said line whereby the polarityresponsive means in idle transmitters connected to the'other of saidconductors'be- "comes e'fiective to disable said last-mentioned idletransmitters, means for driving each transmitter until a complete alarmsignal is transmitted, means responsive to said driving means forrestoring the normal connections of said transmitters to, saidconductors whereby said line is again rendered completely operative andmeans responsive to said restoration for restoring the normal connectionof said source whereby the li'n'e'is available to all transmitters.

MANFRED 'MUEHT'ERL

